This invention relates to wire guides having a Doppler mechanism for determining in vivo flow velocity of a biological fluid. In particular, it relates to a flexible, steerable, fluid velocity measuring wire guide which is receivable in a catheter and positionable sub-selectively in the coronary arterial tree for diagnosing heart disease.
Coronary artery disease is a common medical problem, particularly in the United States, and often manifests itself as a constriction or stenosis in the arterial tree. Coronary artery disease can lead to increased arterial stenosis and gradual diminution of reactive hyperemic response. Because arterial disease is commonplace, it is important to properly diagnose the presence of specific lesions or vessel stenosis and to properly evaluate the efficacy of treatment of these arterial lesions.
Stenoses past the coronary ostium are not only difficult to identify and treat, but are also prime concern because of their effect on available coronary vasodilator reserve. To identify coronary disease, the arteriogram has long been used to determine the presence and extent of stenoses. Applicant's co-pending application Ser. No. 775,857 (incorporated herein by reference) discusses the inadequacies of the arteriogram as an indication of the presence and nature of coronary arery disease. See, White, et al., Interpretation of the Arteriogram, 310 New Eng. J. Med. 819-824, (1984).
Transluminal angioplasty (enlargement of the lumen of a stenotic vessel using an intravascular catheter) was initiated by Dotter and Judkins in the mid-1960's. However, prior to the work of Gruentzig (mid-1970's), coronary stenoses were usually treated by open heart surgery, such as coronary artery bypass surgery. Gruentzig developed an inflatable non-elastomeric balloon mounted on a small catheter which could be introduced into the vessel across the stenoses, and then inflated with a sufficient force to enlarge the stenotic lumen. Since the pioneering work of Gruentzig in the mid-1970's, there have been significant improvements in the equipment and techniques developed for his percutaneous transluminal coronary angioplasty (PTCA) procedure. In the United States, the growth in the number of PTCA procedures being performed has been dramatic--approximately 1,000 PTCA procedures were performed in 1980 and over 100,000 procedures were performed in 1986. PTCA procedures represent a major alternative to bypass surgery and have enjoyed an increasing success rate.
Although PTCA procedures have become increasingly successful, a major cause of failures is the inability to accurately identify the regions of stenoses and to evaluate the success of the angioplasty across the stenotic vessel. That is, the arteriogram is still the prime method of identifying and evaluating the stenosis and can lead to any number of mistakes in interpretations --such as observer error, superselective injection, pulsatile injection of contrast media, total occlusion, etc. Further, angiographic evaluation of the region of stenoses after the PTCA procedure is often difficult, owing to the poor definition of the vessel after angioplasty. Thus, while such coronary angioplasty techniques have been relatively successful in treating the regions of stenosis, the unreliability of the arteriogram has been a significant detraction from the efficiency of angioplasty.
Because a PTCA procedure uses a steerable guide-wire to place the angioplasty balloon catheter sub-selectively in the coronary vessels, it would be a significant advance in the art and a major improvement over the arteriogram if a guidewire were devised which was capable of getting a direct indication of blood flow in a particular region of the coronary vessel. Further, it would be a significant advance if such a guidewire capable of measuring fluid velocity were devised which was useful in measuring velocity of other biological fluids and was easily positioned in a biological vessel of interest.
The velocity determining wire guide of the present invention provides one solution for subselectively identifying the nature and extent of coronary artery disease, and further provides a device which is useful in invasively determining biological fluid flow in any small or constricted vessel. Advantageously, the wire guide of the present invention is of such a size (less than 0.030 inch) that it will easily fit down the central lumen or side channel of an angioplasty catheter which itself is such a size to be subselective in the coronary arterial tree. Preferably, the wire guide hereof is steerable and is useful not only as a probe for locating regions of heart disease, but also as a guide for an angioplasty catheter.